The present invention relates to a method for heating a road by means of a heating installation fed with heat from the ground as well as to a road heating installation for carrying out this method of the type described, for example, in the German Pat. No. 31 43 237.
The transfer of heat energy by heat pipes is dependent on the temperature behavior of the heat carrier medium present in the heat pipe and the temperature gradient between the condensation and evaporation zone of the heat pipe. With the use of heat pipes for heating roads the heat carrier is so selected that it evaporates under heat absorption at the relative constant temperatures prevailing in the depth of the ground and gives off this heat to the road by condensation in the condensation zone of the heat pipes disposed directly below the road surface at slightly lower temperatures but still lying above the freezing point, whereby the condensate flows back preferably under gravity influence to the evaporation zone located deep within the ground. With non-controllable heat pipes the circulatory process, which results thereby, continues for such length of time as the temperature gradient necessary for the evaporation and condensation of the heat carrier medium exists. During winter periods it can be assumed that the heat pipes are in operation over relatively long periods of time and also when a heating of the road would not be necessary as such, namely for example, at temperatures below the freezing point and with a dry road--at the so called dry-cold. A heating of the road can be dispensed with, of course, also at temperatures above the freezing point. However, the heat energy stored in the ground is thereby used up under certain circumstances prior to the termination of the cold period.
In order to assure the operability of a road heating installation also with exhausted ground heat or at extremely cold temperatures the aforementioned German Pat. No. 32 43 237 suggests to connect the heat pipes heat at their lowest place conductingly with an external heat source. However, it is not possible thereby to prevent a premature exhaustion of the heat stored in the ground.
A heat pipe is described in the U.S. Pat. No. 3,958,627 which is controllable in its heat transfer capacity by the blocking of its condensation zone by means of an inert gas. A reservoir tank of constant volume and filled with an inert gas is thereby assembled directly to the heat pipe whereby the inert gas is in communication by way of a continuously open inlet with a condensation zone of the heat pipe. The greater the heat quantity supplied to this heat pipe at its evaporation zone, the more the inert gas is pushed back into the reservoir tank and the more the condensation zone of the heat pipe blocked by the inert gas is released. A control of the heat transfer capacity is therefore possible with this heat pipe only indirectly by way of a change of the heat quantity supplied to the evaporation zone. A self-regulating effect, so to speak of, of the heat pipe is to be achieved thereby.
It is the object of the present invention to further improve the road heating installation supplied with ground heat described in the German Pat. No. 31 43 237 to the extent that a heat removal from the ground takes place only in case in need and thus an unnecessary use-up of the heat energy stored in the ground is avoided.
The underlying problems are solved according to the present invention from a method point of view in that the heat transfer capacity of the heat pipes is blocked during a dry cold by a quantity-regulated introduction of inert gas into the condensation zone of the heat pipes and the blocking is lifted by the also regulated return thereof out of the condensation zone with changing prerequisites. From an apparatus point of view the underlying problems are solved according to the present invention in that the ends of the condensation zones of several heat pipes disposed adjacent one another which are located within the area of the road are connected at least indirectly fluidically in parallel with a gas line and the latter is connected to a reservoir tank for the inert gas. By reason of the supply of the inert gas which is controllable as regards quantity directly from the outside, into the condensation zone of the heat pipe, it is possible to block the condensation zone up to a point of complete blockage and thus to render the heat pipe inoperable with a dry cold or at temperatures above the freezing point. The ends of the condensation zones of several heat pipes disposed adjacent one another which are located within the area of the road are connected at least indirectly fluidically in parallel with a gas line and the latter is connected to a reservoir tank. In this manner up to about 100 heat pipes can be combined into a controllable unit and can be supplied with inert gas from a single reservoir tank, for example, with nitrogen.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, two embodiments in accordance with the present invention, and wherein.